Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
Wind turbine rotor blades generally include a body shell formed by two shell halves of a composite laminate material. The shell halves are generally manufactured using molding processes and then coupled together along the corresponding ends of the rotor blade. In general, the body shell is relatively lightweight and has structural properties (e.g., stiffness, buckling resistance, and strength) which are not configured to withstand the bending moments and other loads exerted on the rotor blade during operation. In addition, wind turbine blades are becoming increasingly longer in order to produce more power. As a result, the blades must be stiffer and thus heavier so as to mitigate loads on the rotor.
To increase the stiffness, buckling resistance, and strength of the rotor blade, the body shell is typically reinforced using one or more structural components (e.g. opposing spar caps with a shear web configured therebetween) that engage the inner surfaces of the shell halves. The spar caps may be constructed of various materials, including but not limited to glass fiber laminate composites and/or carbon fiber laminate composites. Such materials, however, can be difficult to control, defect prone, and/or highly labor intensive due to handling of the dry and pre-preg fabrics and the challenges of infusing large laminated structures.
As such, spar caps may also be constructed of pre-fabricated, pre-cured (i.e. pultruded) composites that can be produced in thicker sections, and are less susceptible to defects. In addition, the use of pultrusions in spar caps can decrease the weight thereof and may also increase the strength thereof. Accordingly, the pultruded composites can eliminate various concerns and challenges associated with using dry fabric alone. As used herein, the terms “pultruded composites,” “pultrusions,” “pultruded members” or similar generally encompass reinforced materials (e.g. fibers or woven or braided strands) that are impregnated with a resin and pulled through a stationary die such that the resin cures or undergoes polymerization through added heat or other curing methods. As such, the process of manufacturing pultruded composites is typically characterized by a continuous process of composite materials that produces composite parts having a constant cross-section. A plurality of pultrusions can then be joined together to form the spar caps and/or various other rotor blade components.
Thus, spar caps formed using pultrusions usually include pultrusion-formed layers bonded together via a resin material. More specifically, spar caps are generally formed of a plurality of stacked pultruded plates that are bonded together in a mold.
Though the benefits of using pultruded plates in spar caps have been realized, inherent properties of such plates or layers present design challenges. For example, using plate-shaped pultrusions to form curved-shaped components. More specifically, many pultrusions have a flat cross-section (e.g. are square or rectangular) as such shapes are easy to manufacture. Though the use of flat pultrusions can offer a significant improvement in cost and producibility of rotor blade components, such pultrusions do not typically lay into curved molds without gaps between the pultrusions and the mold shape. Since wind turbine blades are often curved from root to tip, challenges exist to form pultruded layers that curve with the blade shell. When plates containing different fibers are utilized in the same component, modulus mismatch can become problematic. For instance, substantial differences in the elastic modulus between plates can cause delamination to occur between the plates.
Conformance to the mold can be achieved to a certain degree by cutting the pultrusions into thinner strips; however, this increases the cost of the pultrusion process, machining time, and/or the difficulty of placing the pultrusions into the mold. In addition, the use of pultruded layers creates a concern for crack propagation. More specifically, cracks in a pultruded layer tend to migrate from end to end in a relatively short amount of time.
Accordingly, the art is continuously seeking new and improved methods of manufacturing rotor blade components, such as spar caps, using pultrusions. More specifically, methods of manufacturing rotor blade components using pultruded rods that provide more flexibility to the component such that the component can adhere to curved surfaces of the rotor blade would be advantageous. A crack in a rotor blade component utilizing pultruded rods tends to move in a zig-zag manner around the pultruded rods, which leads to a longer propagation life.